1. Field of the Invention
The present invention relates to a lens barrel, and more particularly to a whole group focusing structure capable of performing focus and zoom, the whole group focusing structure is not only small and low cost, but also has good zooming and focusing effect.
2. Description of the Prior Art
Since the image taking lens assembly has an increasingly wide range of application, particularly for the mobile phone, the image taking has become one of the necessary functions. Nowadays, a mobile phone is usually equipped with a solid image sensor and an image taking lens assembly, such as CCD sensor (charge coupled device) or CMOS sensor (Complementary Metal Oxide Semiconductor). To comply with the requirement of miniaturizing the solid image sensor and the image taking lens assembly as well as improving the performance thereof, four-piece lens assembly in the products needs to be miniaturized and its performance thereof also needs to be improved. Therefore, with the popularization of photographic mobile phone, the research and development of the whole group focusing structure is becoming more and more urgent. Hence, how to develop a whole group focusing structure more satisfying the user's requirements has become an important consideration of the manufacturer.
U.S. Pat. No. 6,369,956 published on Apr. 9, 2002 discloses a two group zoom lens barrel that comprises a plurality of rotary cylinders and linear movement cylinders, two lens groups are connected to different linear movement cylinders. The rotary cylinders drive the linear cylinders to move in the direction of the optical axis, so as to change the distance between the two lens groups. This type zoom lens barrel is simple and small, however, it still has the following problems:
This conventional two group zoom lens barrel utilizes tracks to change the distance between the linear movement cylinders, when a predetermined zooming position is reached, the lenses in different linear movement cylinders are affected by the factors of light, angle, temperature, distance and refraction, the two lens groups in different linear movement cylinders are not at optimum focus position. This conventional two group zoom lens barrel only can focus at predetermined positions and is unable to perform more precise focusing operation. Therefore, such structure still has problem in image quality.
In view of this, currently a three group lens barrel appears on the market, which is formed by adding a third lens group at the rear of the two group zoom lens barrel, and a second drive motor is used to move the third lens group by cooperating with a focal length sensing and controlling system. When the two group zoom lens barrel is zoomed and positioned, the displacement of the third lens group can make the conventional focus point more accurate. Although the abovementioned technology can refocus after zooming operation, it still has the following problems:
Firstly, the zoom mechanism of such three group lens barrel must control three lens groups, therefore it is large and complicated.
Secondly, such three group lens barrel has two sets of control system and two drive motors, the two drive motors not increase the cost but also are difficult to be controlled.
Furthermore, zooming and focusing operation of this lens barrel are controlled separately, so it is much more difficult than conventional controlling methods.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.